Inside the red box are the controls for the 2067. These include the On/Off - System Volume - Tone Control (green arrow), Master Speaker Volume (blue arrow), Audio Selector Switch (red arrow) and Intercom Control Switch (yellow arrow).
The tangle of wires is always a challenge on these types of models. The wires and the solder connections can become brittle where they are attached to the controls. With the flexing that happens to the wires while working on the chassis can cause weak joints to come loose.